ABSTRACT
Visual object agnosia is a marked, modality-specific deficit in visual object recognition which may occur following brain damage.1 The classification of visual agnosia typically conforms to the classical distinction first made by Lissauer (1889), between apperceptive and associative agnosia (e.g., see Kertesz, this volume, Chapter 6; Ratcliff & Newcombe, 1982; Warrington, 1982, 1985, for some recent examples). Apperceptive agnosia is thought to be due to a disability in the construction of a stable representation of visual form, which impairs all high-order recognition processes. Associative agnosia is thought to reflect a deficit in accessing semantic (associative and functional) knowledge about an object following the derivation of an intact perceptual representation of visual form. Both types of agnosia are defined in the presence of what are thought to be intact elementary perceptual functions such as the detection of light intensity, acuity and (at least in some cases) hue.
